1. Field of the Invention
The present invention relates to solid phase extraction, and particularly to the micro-solid phase extraction of haloacetic acids from aqueous solution using an iron-modified rice husk sorbent for precise and selective determination of haloacetic acids (HAAs) in water matrices.
2. Description of the Related Art
Haloacetic acids (HAAs) are the second most prevalent group of disinfection byproducts in chlorinated water, such as swimming pool water, after trihalomethanes (THMs). Recent research has shown that HAAs levels in the pool water are of interest, since their formation and presence has been linked to cancer. They are highly water-soluble and are toxic to humans and plants. Because of their potential carcinogenotoxity, the U.S. Environmental Protection Agency (U.S. EPA) has reduced the maximum contamination level of some regulated HAAs from 0.060 mg/L to 0.030 mg/L. The World Health Organization (WHO) has also set the qualitative target levels for HAAs at 80 μg/L for dichloroacetic acid and 100 μg/L for trichloroacetic acid. HAAs are generally difficult to determine because of their strong acidic and hydrophilic character. There are nine haloacetic acid congeners that contain chlorine or bromine, five of which are regulated and four unregulated. The regulated HAAs are monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), monobromoacetic acid (MBAA) and dibromoacetic acid (DBAA). The unregulated HAAs are bromochloroacetic acid (BCAA), bromodichloroacetic acid (BDCAA), chlorodibromoacetic acid (CDBAA) and dibromoacetic acid (DBAA). The current U.S. EPA approved methods for HAA analysis are EPA methods 552.1, 552.2 and 6251, all of which involve cumbersome liquid sample preparation, or even derivatization, prior to gas chromatography (GC) analysis.
EPA Method 552 and EPA Standard Method 6251 suffer low detection limits at the cost of inept and lengthy extraction-derivatization procedures. EPA Method 552.1, which employs ion-exchange derivatization followed by GC analysis, would be a better option, as it uses less solvent, but it suffers from an increased detection limit. Typical analysis time for the above methods range from three to four hours, and few analytes are detected. Several researchers have capitalized on the limitations of the U.S. EPA methods to develop alternative techniques. However, most of them still require derivatization prior to GC analysis. Interestingly; due to the ionic nature of HAAs, alternative methods (such as liquid chromatography, ion chromatography, and capillary electrophoresis) that do not require derivatization have been explored with marked success. Electron Spray Ionization-Mass Spectrometry (ESI-MS) provides excellent sensitivity and selectivity, but high cost precludes its widespread use. Detection limits of these methods have been found to be significantly greater than the GC methods. Conventionally, liquid-liquid extraction (LLE) and solid-phase extraction (SPE) are the most common sample preparation techniques for HAA analysis. However, the multistep sample extraction and clean up procedures involved require voluminous solvents, are tedious, time-consuming, and lead to analyte loss. Generally, most current methods used in the determination of HAAs in water matrices suffer greatly from increased time for sample pretreatment and degradation of unstable species. Porous membrane-based liquid phase microextraction (LPME) techniques have been explored for good analyte enrichment properties. However, the solvents available for extracting both polar and semi-polar compounds are limited.
In previous years, a sorbent based solid phase microextraction (SPME) technique has emerged as a promising technique for preconcentration of HAAs, although its success is tempered by drawbacks associated with high cost, fragility, and carry-over effects of the fiber. Recently, a dispersive micro-solid phase extraction with ionic liquid-modified silica for the determination of organophosphate pesticides in water by UPLC-PDA detector was ratified, and it demonstrated the precise and sensitive determination of the target analytes. Micro-solid phase extraction technique has shown great promise, since it is robust, durable and capable of reusability. The device does not suffer from carry-over problems, and is easy to prepare in-house at a reasonable cost. Application of the technique for HAA concentration and separation from aqueous solution would be desirable.
Thus, a micro-solid phase extraction of haloacetic acids solving the aforementioned problems is desired.